The present invention relates, in general, to semiconductor structures and, more particularly, to such structures having a barrier layer of titanium.
Diffusion barriers are typically used in semiconductor manufacturing when it is desired to prevent diffusion of certain materials used to form various conductive, semiconductive, or insulating layers of a semiconductor device. An example of one situation where it is desirable to prevent such diffusion is the formation of metal contacts to silicon, such as in a platinum to silicon contact. In the absence of a diffusion barrier between the platinum and silicon, platinum atoms diffuse into the bulk silicon material and silicon atoms diffuse into the bulk platinum material. Further, at the elevated operating temperatures typically used for semiconductor devices such as some chemical sensors, the platinum and silicon will diffuse and react to form platinum silicide at the contact interface. This diffusion and reaction severely degrade the quality of the contact, including an increase in contact resistance.
Also, in certain chemical sensor applications the sensor will be exposed to an oxygen-containing ambient. In the absence of a diffusion barrier, oxygen from the ambient being sensed can diffuse into interior portions of the sensor containing silicon and chromium, which can be oxidized by this diffused oxygen.
Accordingly, it would be desirable to have a diffusion barrier that would prevent diffusion of metals, silicon, and oxygen while maintaining contact integrity, including during operation at elevated temperatures.